Poly(acrylic acid) grafted montmorillonite as novel fillers for dental adhesives: Synthesis, characterization and properties of the adhesive
Laleh Solhi , Mohammad Atai *, Azizollah Nodehi , Mohammad Imani , Azadeh Ghaemi , Kazem Khosravi
* Iran Polymer and Petrochemical Institute (IPPI)Tehran, Iran.
Objective: This work investigates the graft polymerization of acrylic acid onto nanoclay platelets to be utilized as reinforcing fillers in an experimental dental adhesive. Physical and mechanical properties of the adhesive and its shear bond strength to dentin are studied. The effect of the modification on the stability of the nanoparticle dispersion in the dilute adhesive is also investigated.
Materials and methods: Poly(acrylic acid) (PAA) was grafted onto the pristine NaMMT nanoclay (Cloisite® Na+) through the free radical polymerization of acylic acid in an aqueous media. The resulting PAAgnanoclay was characterized using FTIR, TGA and Xray diffraction (XRD). The modified nanoclays were added to an experimental dental adhesive in different concentrations and the morphology of the nanoclay layers in the photocured adhesive matrix was studied using TEM and XRD. Shear bond strength of the adhesives containing different filler contents was tested on the human premolar teeth. The stability of nanoclay dispersion in the dilute adhesive was also studied using a separation analyzer. The results were then statistically analyzed and compared.
Results: The results confirmed the grafting reaction and revealed a partially exfoliated structure for the PAAgnanoclay. Incorporation of 0.2 wt.% of the modified nanoclay into the experimental adhesive provided higher shear bond strength. The dispersion stability of the modified nanoparticles in the dilute adhesive was also enhanced more than 25 times.
Significance: Incorporation of the modified particles as reinforcing fillers into the adhesive resulted in higher mechanical properties. The nanofiller containing bonding agent also showed higher shear bond strength due to the probable interaction of the carboxylic acid functional groups on the surface of the modified particles with hydroxyapatite of dentin.
Keywords: Dental adhesive , Nanoclay ,Graft polymerization, Poly(acrylic acid) , Adhesion properties
dental materials 28 (2012) 369-377